coordinated with those of the other programs; e.g., field experiments will be planned in advance so that maximum outcome will be achieved with minimum resources, and a result from a process study will be integrated into a climate model. Furthermore, the IARC will aim at supplementing other programs; i.e., more resources will be allocated to the important areas in which case these programs have any lack of resources.
C. Scientific Background
The Arctic climate system has shown clear variabilities with various time scales, from seasonal to interdecadal. Its unique characteristics obviously plays an important role in the climate change: sea ice and snow reflect short-wave radiation providing positive albedo feedback for climate change, while the ice cover works as an insulator for the relatively warm ocean. The formation of sea ice results in the brine rejection, which yields a water mass characteristic of high latitude regions. In the shelf regions, this process is responsible for the sinking of water mass along the continental slope. Therefore, it is the key to the strong stratification present in the Arctic Ocean which acts to maintain the large area of the permanent ice cover.
The Arctic Ocean has an important role for the global ocean. Deep water formed in the Greenland Sea is the largest water source of the global ocean, while its formation rate has been found to be reduced in the last decade. It appears that the ice exports, from the Arctic Ocean to the convective regions, prevent deep convection. Hence, they influence the large scale thermohaline circulation of the global ocean. The surprising change that has recently been found is the further intrusion of the Atlantic Water into the intermediate depth of the Arctic. This intrusion may yield significant reduction of the ice cover and make the upper Arctic water lighter. As a result, the larger density difference between the Arctic and the Greenland Sea will increase the Atlantic water inflow. Thus' the Arctic becomes warmer through this positive feedback. A possible outcome would be a fresh water anomaly in the Greenland Sea.
The clouds play an important role in the heat balance of the Arctic. The low stratus prevents outgoing long-wave radiation in the Arctic region, where its formation needs vapor transportation from the ocean. During the summer season, the short-wave radiation melts sea ice, causing melt pond to spread. Snow disappears on the land, while the surface of the permafrost melts. On the other hand, in the winter season open leads within the Arctic ice cover are sources of vapor and heat. The land and the ocean surfaces, as the boundary condition, have effects on atmospheric general circulation, such as wind patterns and the atmospheric boundary layer. In this way, snow and sea ice interact with the atmosphere and clouds, forming a sophisticated coupled system.
The Arctic atmosphere obtains heat and vapor by mixing with the subarctic atmosphere. The meandering jet streams promotes this transportation. It is known that the meanders are induced by zonal variations in the heat sources and the orography. The sea-ice distribution in the high latitude oceans, such as the Barents Sea, varies greatly from year to year, yielding temporal variations in the heat sources. It is likely that the jet stream brings feedback to the sea ice cover. However, it has not yet been clarified how the atmospheric circulation interacts with the distribution of sea ice.
The Arctic climate system, previously mentioned, is suggested to be tackled as follows: climate variabilities will be described based on historical data. Several ambiguous, but important processes in the Arctic are chosen as targets to be clarified. Theoretical and numerical models are developed to understand these processes and to interpret potential observations. These processes will be either included or parameterized in atmosphere and ocean general circulation models. The Arctic models will give useful insights into a global climate prediction model.
The bio-geochemical processes are not only controlled physically, but also give reaction to climate change; e.g., global warming as a result of the carbon cycle. An important process in the high latitudes is related to the phytoplankton which grows on sea ice: i.e., ice algae. The growth of the plankton removes carbon dioxide from the ocean efficiently and influences the distribution of sulfur compounds in the atmospheric boundary layer. In this way, it is very possible that the bio-geochemical aspects modify the atmospheric compounds, which play an important role in the climate change, such as the carbon circulation and the formation of aerosol.
The Arctic land is covered by glaciers, permafrost, tundra and boreal forests. Their distributions vary in response to the climate change; e.g., as global warming leads to melting of glaciers and permafrost. These changes are not only considered important on the ecological and social systems, but they also feedback on physical phenomena, such as a heat balance and hydrologic cycle. In addition, the changes act on social economy. Forest fires impact ecological systems and also affect atmospheric compounds. Although a field observation is inevitable to clarify bio-geochemical processes, satellite remote-sensing is becoming a useful method to document spatially distributed environmental change, permitting extrapolation of in-situ observations to vast regions.
Once global warming and ozone depletion take place, the stratosphere in the Arctic may become colder due to the radiation balance and global atmospheric circulation. The middle atmosphere is an integral part of the earth and interacts with the stratosphere and the troposphere in various ways, and hence, the Arctic middle atmosphere may be highly sensitive to global change. Tropospheric disturbances propagate upward, being manifested as wavy structures of the noctilucent clouds which appear at an altitude of about 80 km. The noctilucent clouds partly consist of CO2-ice as important indicators of the abundance of CO2. The Arctic upper atmosphere has uniqueness of receiving the high solar wind energy. In winter, this energy input can exceed the solar blackbody radiation input. Since the solar energy is greatly variable, its effects should be studied in the field of space weather.
D. Other Programs
Various international collaborative programs and U.S. programs have been carried out, aiming at the further understanding of climate change in the Arctic and subarctic regions. Many more programs are currently under planning. The IARC should cooperate with them as one of the members in the international Arctic research group, Furthermore, some
